The present invention relates to plasma display panels and more particularly to an improved conductor configuration to compensate for the reduced operating margin resulting from the use of interstitial spacer elements in plasma display devices.
In plasma display devices, parallel conductor arrays are formed on a pair of glass plates, overcoated with a dielectric and a dielectric protective layer and the plates then sealed into an envelope filled with an ionizable gas under pressure with the conductor arrays disposed substantially orthogonal to each other, the conductor intersections defining the individual gas discharge cell electrodes. One of the critical parameters in such display devices is the discharge or chamber gap, ie, the distance between opposite walls of the cells, which must be maintained substantially uniform across the entire surface of the display panel, a particular problem in large size panels of high resolution. Such gaps in smaller display devices are generally provided by spacer rods which are positioned about the periphery of the panel. However, in large size panels, it is necessary to utilize in addition a configuration of interstitial spacer elements within the panel display area, such spacer elements being in the form of metallic rods which are interspersed between adjacent conductors on one of the plates. The referenced copending Application Ser. No. 841,186 relates to an interstitial spacer system for a plasma display panel in which a plurality of metallic spacer elements are positioned at the predetermined locations on the screen to provide and maintain a uniform discharge gap. One problem associated with interstitial spacers is they affect the performance of the adjacent cells. When a spacer is placed between two normal cell lines or electrodes, it caused the voltage level of the spacer element to be shifted upward. Stated another way, it distorts the electric field intensity for the discharge cells adjacent the spacer element and the field strength is thus reduced. As a result, these cells will not turn on when the panel is operated at the normal sustain voltage, or if turned on, will extinguish rapidly. While the spacer elements are designed to fit between conductors and the technology to bond the spacer element to one of the dielectric surfaces is available, failure of cells adjacent to the spacer elements such as described above frequently occurs, when the electrical parameters of those conductors adjacent the spacer elements are altered.
The primary electrical parameter of plasma display devices is the panel margin, defined as the difference between the maximum and minimum sustain voltage at which all cells are required to sustain only a single cell. This parameter, designated V.sub.s max.-V.sub.s min., required a nominal margin of approximately 10 volts for operation. However, when metallic spacers are positioned within a panel, both the maximum and minimum sustain voltage of cells immediately adjacent the spacers shift upward dynamically although at differing rates, reducing the margin by 30-40% volts. In addition to difficulty in turning such cells on, those cells which are turned on extinguish more readily, producing clusters of off cells adjacent the spacer areas which are cosmetically undesirable. Such cells also constitute the weak points in a panel, and are susceptible to premature aging. Thus there exists a requirement to compensate for any modification of the characteristics of conductors adjacent to spacer elements whereby all cells, including those adjacent the spacer elements, may be driven with the same signal levels.